1. Field of the Invention
This disclosure relates to the field of oilwell stimulation, drilling, and recovery. In particular, the present disclosure relates to an apparatus and method for injecting biocide into a tank to treat oilfield water or oilfield fluid. More particularly, the present disclosure is directed to an apparatus and a method for injecting biocide at a position near the bottom of a tank. Also disclosed is a method of efficiently treating a plurality of tanks with biocide.
2. Background of the Invention
As is well-known to those skilled in the art, the presence of microbiological contaminants in liquid systems causes problems typified by increased corrosion rates and plugging of conduits, filters, pumps, etc. During petroleum production, it is often desirable to inhibit microbiological growth in substrates which include aqueous or aqueous-hydrocarbon liquids found in subterranean well holes, in surface ponds or reservoirs of crude oil, in salt water separated from crude oils, and on the various metal equipment which comes into contact with these fluids. Such equipment includes tanks, pumps, structural members, etc.
Natural and synthetic polymers are used in the oil industry in methods of well stimulation, drilling, and recovery. These polymers are used, for example, in water flood, fracturing and drilling fluids, and are exposed to an environment that is conducive to the growth of microorganisms. Some of the most favorable environments for bacteria are dirty frac tanks and mixing water. Microorganisms, for example bacteria, feed on polymers (for example, gel stabilizers used in aqueous fracturing fluid processes) by releasing enzymes. The enzymes degrade the polymer to sugar, and the microorganisms absorb the sugar through their cell walls. When conditions are favorable, some species may attain maximum concentrations within twenty-four hours and may be the chief cause of polymer degradation. The growth of microorganisms on the polymers used in these fluids can thus materially alter the physical characteristics of the fluids. For example, bacterial action can deteriorate the polymer, leading to a loss of viscosity and rendering the fluids ineffective for the intended purpose. Fluid degradation may also lead to the formation of a large biomass, which may plug the formation and reduce permeability.
A wide variety of biocides have been used in various environments, for example bactericides are used to control sulfate-reducing bacteria, slime-forming bacteria, iron-oxidizing bacteria and bacteria that attack polymers in fracture and secondary recovery fluids. Biocides should be handled with caution, to prevent personal and environmental contamination. Biocides are, by their very nature, dangerous to handlers. Handlers must avoid eye and skin contact and, when liquid biocides are utilized, must avoid splashing or spilling the liquid biocide, as spilled biocides can contaminate potable water sources.
Often, tanks are treated with biocide to inhibit microbiological growth. Commonly, biocide is introduced into the tank to be treated by being dropped into the top of the tank. This treatment routinely involves a handler climbing to the top of the tank (or truck), which may be 12 feet to 16 feet high, in order to ‘drop’ the biocide into the tanks. This climbing inherently creates a danger of falling, especially in inclement weather and when there are no latches available for the use of a safety harness. Attachments to ladders and to the tops of tanks that would be necessary to enable a safety harness to be latched are easily damaged during loading/unloading of the tanks, and make positioning the tanks on location very difficult. The footpad available for placing multiple tanks often mandates placing the tanks in close proximity. This negates the practicality of such attachments for latching a safety harness. Furthermore, cranes, hoists, etc., are not normally available on location during these operations and are not economically viable to use as a safe work platform. When tanks are located in close proximity to each other, it is not uncommon for the handler dropping the biocide to climb to the top of an outer tank and hop from tank to tank in order to introduce the biocide into the desired tank. This unsafe practice becomes even more dangerous when the tank to be treated is difficult to get to and when weather conditions, such as snow, wind and rain, exacerbate the difficulty of reaching the treatment tank.
Accordingly, an ongoing need exists for an apparatus and a method for treating a tank with biocide that minimizes the possibility of contamination of the environment and eliminates the risk of injury to or death of a handler from falling a distance during treatment of the tank.